The term low emissivity glass is defined to mean glass which is formed such that it has low emissivity by sputter deposition of electrically conductive metal such as silver. The low emissivity glass is also defined to mean functional glass which has an effect of energy savings of buildings by reflecting solar radiant heat in the summer and preserving energy of infrared light emitted by space heaters in the winter due to specific coatings on a surface of the glass substrate.
As prior art methods of producing the low emissivity glass described above, a method of making a chamber under an oxygen atmosphere by injecting a selected amount of oxygen gas into the chamber and then depositing a dielectric layer on a low emissivity layer by using metal material as a target material, has mostly been used.
The dielectric layer is generally formed by depositing a dielectric thin film comprising a metal oxide on one or both surfaces of the low emissivity layer, so that the dielectric layer is mainly used for the purpose of preventing oxidation of silver contained in the low emissivity layer and improving visible light transmissivity.
In the conventional techniques, metal oxides such as zinc oxide, titanium oxide, tin oxide, and composite metal oxide of tin oxide and zinc oxide are commonly used as those contained in the dielectric layer. However, there have existed problems that the dielectric layer comprising the above mentioned metal oxides is limited in its use in the field in which high visible light transmissivity is necessary because of a relatively low refractive index and that the productivity thereof is lowered because of a low deposition rate at the time of sputter deposition.